1. Field of the Invention
The present invention relates to hypodermic syringes with a safety sheath, wherein the safety sheath automatically extends over the needle of the syringe after the syringe has been used.
2. Description of Prior Art
It is well known that many serious diseases, such as Acquired Immune Deficiency Syndrome and Hepatitis can be spread or transmitted by blood or other bodily fluids. It is a major concern to health care workers who administer medications using hypodermic needles, that the needles may accidentally stick or prick the health care worker transmitting a disease from a patient to the health care worker. This can happen, for example, when the patient pulls back suddenly upon insertion or removal of the needle, or when the needle is being handled for disposal.
In order to prevent such accidental needle sticks or pricks, many inventions have been made which provide a protective sheath that covers the needle. In some cases, the sheath has to be manually removed or replaced over the needle. Such safety syringes are problematic, because it is very easy to stab or stick oneself in the hand trying to remove or replace the sheath. In other cases, the sheath is slidably mounted on the syringe to uncover and cover the needle. Bias means are often employed to urge the sheath into the extended or covering position. While this is an improvement over a manually removable sheath, in many cases, some type of locking or latching mechanism is employed to retain the sheath either in the retracted or extended position. Such a locking mechanism again must be manually actuated with the hand or fingers, exposing the hand to accidental pricks while manipulating the mechanism.
Some safety syringes have protective sheaths that do automatically extend after the syringe is used, thereby preventing the need to manually engage a locking mechanism. In such syringes, the extending sheath is triggered by the advancement of plunger into the syringe barrel. Such prior art safety syringes are exemplified by U.S. Pat. No. 5,376,080 to Petrussa, entitled SINGLE USE RETRACTABLE NEEDLE SYRINGE. The problems associated with such prior art safety syringes is that since the sheath extending mechanism is triggered by the use of the syringe and not by direct manipulation, the sheath extending mechanism tends to be of a complex design. This makes such safety syringes both difficult and expensive to manufacture.
It is therefore and objective of the present invention to provide a safety syringe with a safety sheath that automatically extends over the needle of the syringe after the syringe is used.
It is a further objective of the present invention to provide a safety syringe with an automatically extending sheath that is low cost, easy to manufacture and simple to operate.